1. Field of the Invention
The present invention relates to a linear stepping motor, especially for a new-type secondary structure of a linear stepping motor and its manufacturing method.
2. Description of the Prior Art
Linear stepping motors are applied in industry widely. For example, some equipment such as a wafer clamper and a high-speed wafer scanner, is equipped with linear stepping motors and act due to excitation between the primary and secondary of linear stepping motors. Commonly used secondary structure of the linear stepping motor is usually manufactured by milling or etching teeth. Teeth milling and etching have the following disadvantages, respectively:
1. Disadvantages of milling teeth
(1) It is uneasy to manufacture: For the sake of shortening the displacement of each step to improve the resolution of the stepping motors, tooth grooves are usually thin and deep so that the special-purpose cutting tool is not easy to be manufactured and is expensive in cost while short in life. Besides, processing rate is slow, and process cost is high;
(2) It is uneasy to measure: After milling teeth, products are not easy to be measured, so expensive apparatus are essential to examine and the quality is not easy to be controlled;
(3) The weight is heavy: The whole solid block of metal is used to be processed, so the product is heavy in weight;
(4) Eddy current: For the sake of using a whole metal block, which is a good conductor, eddy current is produced, while the motor is excited, such that energy is wasted;
(5) Restriction of length and area: The length and area of the secondary structure of the motor are restricted by the working area of the milling-machining frame.
2. Disadvantages of etching teeth:
(1) Process is complicate: Several steps such as washing, photograph development and exposure, and etching, etc, are complicate. Besides, if deeper etching depth is required, longer etching time and higher manufacturing cost are caused;
(2) High pollution: Chemical reactant used for etching accompanies with high pollution, therefore it easily results in environmental problems;
(3) The same situation of heavy weight, restricted area and producing eddy current as in the aforementioned teeth milling occurs for the same reason, using a whole metal block.
The purpose of the present invention is to provide a new-type secondary structure of a linear stepping motor and its manufacturing method. By the design of the present invention, the manufacture of the secondary structure of a linear stepping motor is simpler and cheaper. Besides, both weight and eddy current of the secondary of the linear stepping motor are reduced. Quality control is easier and more efficient. The structure of the new-type secondary structure of the linear stepping motor mainly comprises several permeance sheets and insulating sheets arranged in stagger one by one. The permeance sheets are made of permeance material, which usually is (pure) iron or silicon steel, and so on. The insulating sheets are made of material with poor permeance. Among many common materials with poor permeance, ones still having characteristics of light mass, good combination, sufficient strength and good machinability are resin, glass and glass fiber compound material, carbon fiber compound material. Especially glass fiber compound material, because it""s relatively cheaper in price and better in strength, it is a very ideal material for insulating sheets.
After the permeance sheets and insulating sheets are shaped, and before they are assembled, the secondary structure can be easily measured so that the thickness of the aforementioned sheets can be got and the precision of the tooth shape can be controlled. When the structure is manufactured, the process just comprises arranging the permeance sheets and insulating sheets in stagger one by one and then combining these sheets. Therefore, the manufacture process is very simple. There are many methods of combining the permeance sheets and insulating sheets, for example, pressurizing and shaping, arranging regularly and locking via screws or gluing, etc. For the surface of combined permeance sheets and insulating sheets, colloid is filled into the clearance of the permeance teeth and then the top surface of combined permeance sheets and insulating sheets are ground to get a flat plane to make the slide between the primary and the secondary structure more smooth.
Because the secondary structure of the linear stepping motor can be piled successively, the restriction of length or area of milling or etching teeth of traditional manufacturing methods can be overcome. Besides, the use of the insulating sheets with specific gravity less than metal, the total weight of secondary structure can be lowered to reduce the inertial while the secondary structure serves as a rotor, the lighter weight or smaller inertial yields larger acceleration. In addition, because of the isolation effect of the insulating sheets, less eddy current is produced so that efficiency of the motor is increased and temperature rise is decreased.